Method of decomposing mixed metal-salt solutions



Patented Apr. 24, 1.923.

UNITED 'STATES PATENT OFFICE.

mRY PAULING, F I'BERLIN-GRUNEWALD, GERMANY.

4`'illfliilll. H0129 0F DECOMPOSING MIXED METAL-SALT SOLUTIONS.

I I Application led August 8, 1921. Serial No. 489,835.

To au whom it may concer/n.:

Beit known that I, HARRY PAULrNo, citizen of the State of Prussia, German Repub- 1 1icresiding at Berlin-Grunewald, Hagenstr. :"5`28,g;have invented certain new and useful Improvements in Methods of Decomposing Mixed Metal-Salt Solutions, of which the following is a specification.

Decomposition y of mixed solutions of metal salts has heretofore been effected by subjecting such solutions to electrolysis, utilizing insoluble anodes and limited potential. Such treatment, however, does not result in obtaining each metal salt b itself,

but only the one metal of greater e ectrical conductivity as Such, while the less conductive metal salt remains in the stronglyacidulated solution which can only be treated with difficulty to obtain from it the pure salt of the less conductive metal.

The object of the present invention is to obviate this drawback and to obtain the salts as such and each by itself, either as crystals or in solution. .To effect this object, the

mixed metal salt solution-as for instance a solution of brass in sulfuric acid-is subjected to electrolysis, using as the anode material the more conductive metal (copper) and only such a potential as will deposit that metal on the cathode, care being taken to prevent the anode and cathode solutions from mixing either by superposing them or by making use of an interposed diaphragm. As the cathode solution, the one which is to undergo decomposition is used, while a pure solution of the salt of the more conductive metal serves as the anode solution. In the example mentioned, the brass solution therefore forms the cathode solution, and a solution of pure copper sulfate forms the anode solution. As a resu t of the electrolytic action, the copper of the anode is gradually dissolved and additional copper sulfate is formed which enriches the anode solution,

where the cathode solution is decomposed. Thereby the metal gone into solution at the anode is regained at the cathode which, later on, after reaching a certain thickness, is alwa s used as the anode. The anode materia is therefore required only at the vvery beginning of the electrolysis, as it is always regained from the solution during thefurther course of the operation.

ossible to increase thev amount of.

jected to a crystallizing action by cooling d them after the more conductive metal has been separated.

The process is, of course, also suitable for the treatment of alloys other than brass. It may, for instance, be applied to coppernickel alloys (Monel-metal) and the like. To effect aV saving in the current consumed, it is particularly advantageous to acidulate both solutions somewhat, because in that case the hydrogen-ion forms the chief vehicle for the current in place of the metalion and, in consequence, contributes to separating the ion of the more conductive metal considerably quicker from the cathode solution.

To explain by an example how the process is carried out to decompose, for instance, a mixed solution of zinc sulfate and copper sulfate as obtained by dissolving brass in sulfuric acid with access of air, reference may be had to the accompanying drawing, the single figure of which represents a vertical section through one form of apparatus which may be used. The vessel E, which is provided With a horizontal electrode A forming the anode, and with a horizontal electrode K forming the cathode, both electrodes being of copper, is half-filled-or filled to a point above the anode A-with'a pure copper sulfate solution C. Then the mixed sulfatesolution B to be decomposed is superposed upon the first solution, so that the contact line ofthe two solutions lies between the electrode couple. If now the lec- .trolytic process is commenced, accompanied byappropriate heating, the copper of the anode A is dissolved, while on the cathode K copper is deposited. In other words, the anode solution C is enriched by further copper'sulfate, while the copper sulfate in the cathode solution B disappears.

Care must, of course, be taken to so calculate the current density and potential as to prevent liberation of zinc. ln a neutral solution, the current-output amounts to about 50%, Which is increased to about 85% .if both solutions have added to them a corresponding surplus of free acid, because in that event the hydrogen-ions Willform to a greatly preponderating extent the vehicle for the current, so that only an inconsiderable proportion of copper-ions will pass from the anodic to the cathodic solution. After a certain time, depending upon the current intensity employed, the cathodic solution, i. e., the originally mixed-sulfate solution, is entirely free of copper sulfate, Whereas the anodic solution has become the richer in copper sulfate by the corresponding amount. The two solutions are then siphoned o" se arately from the vessel E. lf the anodic so ution treated was originally a copper sulfate solution saturated in a cold state and then heated to 40 C., and is now cooled, the excess salt-that is, the copper sulfate which Was added toit during electrolysis-Will separate out in the form of crystals, and the mother-liquor can thereafter be re-used on a'new charge. The zinc sulfate solution is either concentrated by evaporation for crystallization or is treated for some other purpose. The electrodes A and K, now reversed in thickness, are'exchanged for a new charge and further electrolysis, as above mentioned.

Exactl the same procedure may be adopted 1n treating mixed solutions of copper sulfate and nickel sulfate, or solutions of the respective chlorides and the like. lf metal salt solutions are to be decomposed, the components of which can be at least partially separated from one another by fractional crystallization, the vessel or container may be lled entirely with the solution to be decomposed. By electrolysis, this solution will become decomposed into' two solutions, While the content of the salt of the more conductive metal in the cathode solution decreases, whereas the content of that salt in the anode solution is correspondingly increased. Then, when the tWo solutions thus obtained are se arately drawn o, and each is subjected to ractional crystallization, that salt which is in excess in each solution is separated, viz. the salt of the more conductive metal is separated from the anode solution and that of the less conductive metal from the cathode solution.-4 The process is, ofcourse, preferably carried out in such a4 manner as to completel deprive the anode solution'o its contents o the salt of the more conductive metal, so that it may be directly and fully treated to obtain the pure salt of the less conductive metal; Whereas the cathode solution is subjected to fractional crystallization and the remaining motherliquor is again subjected tothe above-'described electrolytic process on a new charge.

Leraars lf, for instance, a copper-nickel-sulfate solution is to be decomposed, the solution, before being electrolyzed is subjected tofractional crystallization as long as only pure copper sulfate separates out. point is reached Where nickel sulfate crystals are also formed, then the mother-liquor is sub'ected to electrolysis, as above described. the cathode space its entire content of cop per, While the liquid in the anode space 1s correspondingly enriched with co per sulfate. The copper sulfate thus ad ed t0 the anode solution ma then be obtained by fractional crystallization in a pure state, after which the remaining mother-liquor is again subjected to electrolysis according to the process. The electrodes are, of course, exchangeable in this case as in the case first described.

l claim as my invention: Y

1. The herein-described method, comprising the step of assino` an electric current through a mixe metall salt solution in' a vessel provided with electrodes of the more conductive metal contained in the solution, to electrolytically decompose said solution.

2. rllhe herein-described method, comprising the step of passing an electric current through a mixed metal saltv solution in a vessel/'provided with electrodes of the more conductive metal contained in the solution, to electrolytically decompose said solution, While utilizing such solutionas the cathode solution and a pure solution of the salt of the aforesaid more conductive metal as the anode solution.

3. The herein-described method,.compris through the acidulated solution in a vessel.

provi ed With electrodes of the more con- When they,

The thus-treated liquid loses in ductive metal contained in the solution to electrolytically decompose said solution.-

a. rl`he herein-described method, comprising the steps of passin an electric current through a m'med mete salt solution in a vessel provided with electrodes of the more conductive metal contained in the solution, to electrolytically decompose said solution; and exchanging the electrodes from time to time. y

5. rlhe herein-described method, com rising'the steps of subjectin a mixed met salt solution'to the action o an electric current, in the presence of heat, in a vessel provided with electrodes of the more conductive metal contained in the solution, to i compose said solution into two dierent s0'- lutions, in one of which the 'salt of the ore' conductive metal predominates' and in the dually.; dev l 1,452,813 c j B ing the steps of subjecting a mixed metal salt of the aforesaid more conductive metal salt solution to the action of an electric than the other; and withdrawing the two current in a vessel provided with electrodes solutions-separately from the vessel. l0 of the more conductive metal contained in In testimony whereof thatfI have ahxed u 5 the solution` to gradually decompose said somy signature.

lution into two different solutions, one of which contains a greater percentage of the HARRY PAULING. 

